The present invention relates to a heat shrinkable laminated packaging material. More particularly, it relates to an improvement on a heat shrinkable laminated packaging material having a heat sealability.
Heretofore, heat shrinkable plastic films have been used widely for packing a variety of foods.
Heat shrinkable laminated packaging materials are usually used as materials for heat shrink bag packaging. A laminated packaging material consisting of a heat shrinkable base film and a sealant film laminated on one surface of the base film is made into bags by fin seal method or tape seal method. A laminated packaging material consisting of a heat shrinkable base film and a sealant film laminated on both surfaces of the base film is made into bags by methods such as wrap seal. The obtained bag is filled with hams, sausages, cheeses or other goods, and, after evacuated, the bag is heat sealed. Then the bag is subjected to heat shrink treatment in hot air or hot water to provide a tightly covered package.
In same cases, characteristic properties such as stick-up resistance, cold resistance and oxygen barrier are required for packaging materials, depending upon the kind of goods to be packed. In that case, biaxially stretched nylon films are usually used as the heat shrinkable base film. In the case of the nylon films, however, the oxygen barrier is lowered and the film tends to elongate due to moisture absorption. Therefore, the nylon films are usually used in the form of a laminate wherein a heat sealable and not heat shrinkable sealant film or a moisture proof sealant film is laminated on both surfaces of the nylon film.
Conventional heat shrinkable and heat sealable laminated packaging materials are disclosed in U.S. Pat. No. 4,501,779. However, those packaging materials are a multi-layered film wherein a sealant film having substatially no heat shrinkability is laminated on one or both surfaces of a heat shrinkable base film or a multi-layered film which is prepared by laminating a sealant film on a base film and stretching the resulting laminate.
However, those multi-layered films do not have a sufficient heat shrinkability, since the sealant film of the multi-layered film does not have a good heat shrinkability. When the multi-layered films are used in shrink packaging, they are poor in tightness and voids occur within package, which results in poor appearance due to less tightness. Further, the voids are also a cause for the propagation of bacteria since due-drips tend to be caused therein.
When an attempt that the heat shrink treatment is carried out at higher temperatures is made to overcome the above-mentioned drawbacks, any satisfactory finish appearance is not obtained. Furthermore, some goods packed are deteriorated due to such higher temperature shrink treatment.
It is an object of the invention to provide a heat shrinkable and heat sealable laminated packaging material having an excellent heat shrinkability.
This and other object of the present invention will become apparent from the description hereinafter.